How to Choose Cable Sheath: Corrugated Aluminum vs Copper vs Armored

How to Choose a Sheath: Corrugated Aluminum vs Copper vs Armored Outer Sheath

In underground and industrial power projects, sheath selection is one of the fastest ways to either extend cable lifetime—or create avoidable failures, rework, and downtime. As a manufacturer and supplier, we evaluate sheath decisions the same way our utility and EPC customers do: what will survive the environment, install cleanly, and deliver the lowest total cost over decades.

At a practical level, you are choosing how the cable will resist three categories of stress: moisture ingress, corrosion/chemicals, and mechanical damage (impact, rocks, vibration, rodents, construction). In HV and MV constructions, the sheath decision also affects grounding, fault-current return paths, and electromagnetic compatibility.

If you want to see the sheath structures we commonly supply in high-voltage projects, our 66–500 kV XLPE power cable page summarizes typical options, including corrugated aluminum sheath, copper sheath, and steel armored outer sheath.

What the sheath actually controls (and what it does not)

What it controls

• Water barrier performance (radial moisture ingress and long-term wet aging risk).
• Corrosion resistance (soil chemistry, stray DC currents, chloride environments, industrial chemicals).
• Mechanical survivability (impact, crushing, abrasion, stone backfill, third-party damage).
• Bonding/grounding behavior (continuity, shield currents, fault return capability).

What it does not control by itself

Sheath choice does not “fix” a poor installation method. A perfectly specified sheath can still fail early if bends are too tight, pulling tension is uncontrolled, joints are contaminated, or water is allowed into cut ends before termination. In other words, lifetime is the product of design + accessories + workmanship, not sheath material alone.

Corrugated aluminum sheath: the workhorse for HV underground reliability

Corrugated aluminum sheath is widely used in high-voltage XLPE designs because it provides a strong moisture barrier while maintaining installation-friendly flexibility. The corrugation profile improves bend performance versus a smooth metal tube and helps the cable accommodate thermal expansion and ground movement without concentrating stress at one point.

Where it performs best

• Urban underground transmission and distribution where moisture control is critical (ducts, tunnels, direct-buried with appropriate backfill).
• Projects that need a robust barrier layer without the installed-weight penalty of copper sheath.
• Long route lengths where pulling tension and handling speed matter.

Concrete engineering comparisons you can use

For the same geometry, copper is much heavier than aluminum. As a simple illustration: for a metal sheath ring of 70 mm outside diameter and 2.0 mm thickness, the aluminum sheath mass is about 1.15 kg/m, while copper is about 3.83 kg/m—roughly 3.3× heavier. That weight difference directly increases drum weight, pulling tension, and handling time on-site.

In our HV range, corrugated aluminum sheath constructions are typically paired with XLPE insulation designs commonly rated around 90°C continuous with short-circuit tolerance referenced around 250°C (design- and standard-dependent). For an example of our corrugated aluminum sheath HV construction, you can review our 127/220 kV corrugated aluminum sheath cable page.

Trade-offs to plan for

• Aluminum requires disciplined bonding hardware and anti-oxidation practices at terminations and joints.
• If your site has aggressive stray DC currents or unusual soil chemistry, sheath protection strategy matters as much as material choice.

Copper sheath: premium performance for fault-current, fire, and bonding control

Copper sheath is selected when customers want maximum electrical conductivity for shielding/bonding, robust fault-current handling, and stable performance in demanding service. Copper also supports a broad accessory ecosystem (bonding, grounding, termination methods), which can reduce installation risk on complex projects.

Where copper sheath is the right call

• Critical circuits where grounding continuity and predictable bonding behavior are prioritized (substations, data centers, transit systems).
• Fire-performance driven designs that use inorganic insulation systems and copper sheath to maintain circuit integrity under extreme temperature exposure.
• Installations with high electromagnetic sensitivity where shielding effectiveness is a practical requirement, not a datasheet checkbox.

Examples from our copper-sheath portfolio

For fireproof flexible applications, we supply copper-sheath constructions that use stranded copper conductors and inorganic insulation systems; see our wrinkles copper sheath flexible fireproof cable page for a representative structure.

For mineral-insulated (MI) designs, copper sheath enables very high temperature service and long-life performance in harsh environments. As one durability reference point in MI literature, a 0.25 mm copper sheath is reported to take 257 years to oxidize under 250°C conditions; see our mineral insulated cable page for the full context and typical application advantages.

Trade-offs to plan for

• Higher installed weight (often the hidden driver of labor and handling cost).
• Material cost sensitivity; copper-sheath designs are typically positioned as a premium solution in both CapEx and working-capital terms.
• In certain corrosive environments, copper may still require an additional outer jacket or protective measures, depending on exposure.

Armored outer sheath: when mechanical damage is the real lifetime risk

“Armored outer sheath” is the right conversation when your primary failure driver is mechanical: direct burial through rough backfill, construction zones with frequent excavation, heavy vibration, rodent-prone routes, or cable runs exposed to impact and crushing. Steel tape armor and other armored constructions are fundamentally about physical survivability, not only moisture control.

What armor changes in real installations

• Higher crush/impact resistance and better tolerance to imperfect backfill.
• Larger overall diameter and higher stiffness, which increases bending radius requirements and can slow pulling operations.
• More layers to manage at joints and terminations, which raises workmanship sensitivity.

Typical applications we see from buyers

In MV systems, steel tape armored designs (for example, common “22” constructions) are used where the cable must bear certain external mechanical forces. In our MV range, we also reference service-life expectations exceeding 30 years when selection and installation match the operating environment; see our 3.6/6 kV–26/35 kV XLPE cable page for representative type designations and applications.

In low-voltage systems, steel-tape armored variants are commonly chosen for tunnels, cable trenches, and direct-buried runs where external mechanical forces are expected. You can also reference installation constraints such as bending-radius guidance on our 0.6/1 kV XLPE/PVC power cable page.

Lifetime drivers we design against (and how sheath selection affects each one)

When customers ask us which sheath “lasts the longest,” we usually answer with failure modes first. Below are the practical drivers that typically dominate lifetime in the field.

The key takeaway is simple: the “best” sheath is the one aligned to your dominant risk. If your failure history is water-related, prioritize barrier integrity. If your history is excavation damage, armor usually pays for itself. If your history is grounding or fire, copper-based solutions often reduce operational risk.

Installation realities: bending radius, pulling, joints, and terminations

Bending radius: where design meets field constraints

Armored designs generally increase cable diameter and stiffness, which increases the minimum bend radius you must enforce at rollers, ducts, and termination cabinets. As an example of typical guidance in low-voltage designs, we reference bending radii such as 20× cable diameter for single-core and 15× cable diameter for multi-core constructions (design-specific). Tight bends are a common root cause of hidden jacket damage that later becomes a moisture path.

Pulling tension and sidewall pressure

If your route includes long pulls, multiple bends, or congested ducts, sheath weight matters. Corrugated aluminum sheath helps reduce drum weight and pull loads versus copper sheath at the same geometry, which can reduce the need for intermediate pulling points. For armored designs, it is often smarter to plan additional pulling infrastructure than to “force” the cable through a route that exceeds safe sidewall pressure.

Accessory workmanship: the hidden lifetime multiplier

• For metal sheaths, specify bonding/grounding method early (and keep it consistent across joints).
• Control moisture at cut ends immediately; many long-term insulation problems begin as “temporary” exposure during installation.
• If your project has unusual soil or chemical exposure, require the right oversheath compound and protective measures in the technical specification, not after procurement.

Cost: how to compare quotations without missing the real drivers

Cable buyers often compare sheath options on material price per meter. That is useful, but it is not enough. The real cost difference typically comes from installed cost: handling time, pulling equipment, jointing complexity, route preparation, and the cost of failure risk.

A practical way to think about cost

1. Start with material cost per meter (sheath metal + armor + oversheath compound).
2. Add logistics: drum weight, transport limits, unloading equipment, site storage constraints.
3. Add installation productivity: pulling speed, number of joints, rework probability.
4. Add operational risk: consequence of failure (repair time, outage cost, access difficulty).

If your procurement is competitive-bid, I recommend you compare quotations using the same route assumptions (pull lengths, number of joints, installation method) and treat “cheapest sheath per meter” as a starting point—not the finish line.

A selection checklist you can send with your RFQ

To recommend the right sheath (and quote accurately), we typically ask buyers to include the points below. This prevents mismatched designs that look fine on paper but create installation and lifetime problems later.

• Voltage class and system design (LV, MV 6–35 kV, HV 66 kV and above).
• Installation method: direct burial, duct, tunnel, cable tray, trench, overhead.
• Mechanical risk level: construction traffic, rock backfill, vibration, rodents, crushing exposure.
• Moisture and corrosion exposure: groundwater, coastal chloride, industrial chemicals, stray currents.
• Bonding/grounding expectations and fault-current requirements.
• Route constraints: maximum pull length, number of bends, minimum bend radius constraints, access for joints.
• Target service life and consequence of failure (standard feeder vs mission-critical service).

If you would like a single place to review the product families we supply (HV/MV/LV and specialty cables) before you finalize your RFQ, you can start from our Products page and navigate to the voltage class and cable type that matches your project.